A spacecraft carries a large quantity of electronic equipment on its mission in space. Included amongst that equipment is an RF reflector, typically used as an antenna in the RF communication system, and a solar array, that is used to convert sunlight to electrical power for recharging the spacecraft's storage batteries. The RF reflector is deployable, that is, it folds up into a small package, occupying the smallest volume technologically possible within the spacecraft's precious cargo hold; and, upon command, unfolds to cover a very large area when the space craft is positioned in orbit. Likewise the solar array, formed of photovoltaic cells, is similarly deployable. When deployed, the stowed solar array also unfolds the solar panels which spread over a wide area. As those skilled in the art appreciate, those deployable structures are expensive to manufacture and contributes to the high cost to the space mission.
When large structures such as large deploying reflectors and large area solar arrays share the same spacecraft, they must be properly positioned as deployed so as to avoid shadowing one another. Otherwise the reflector could block some of the sunlight from reaching the photovoltaic cells within the array, reducing electrical performance. Conversely, the structure of the solar array would interfere with passage of RF radiation from and to the reflector, reducing the antenna's performance. To avoid such shadowing, the two structures must be carefully positioned. Many times careful positioning requires additional deployment devices, such as, as example, deployment booms. Those additional deployment devices add weight and necessarily take up precious cargo space on board the spacecraft.
The elimination of deployment booms or other supplementary deployment devices offers a decided advantage for the mission. For one, the weight launch can be reduced, thereby reducing fuel requirements. But, more importantly, the savings in weight and volume can be used for other equipment important to the mission or that increases the number of mission tasks that can be performed during the course of the mission.
Further, should it be possible to integrate the structure of the solar array within the structure of the reflector, then even greater efficiencies accrue. The launch weight for the RF reflector and solar arrays is reduced in weight and storage volume, a decided advantage. And, importantly, the construction cost for a foldable structure should fall, since it is necessary to construct and adjust only a single support structure, instead of two separate ones. By reason of that integration the booms and other additional deployment devices used in the past for the RF reflector and/or solar array should become unnecessary. The present invention offers such integration.
Accordingly, a principal abject of the present invention is to integrate an RF reflector and a solar array into a single deployable structure.
A further object of the invention is to reduce the combined weight and size required in total by use of both an RF reflector and a solar array.
A subsidiary object of the invention is to eliminate deployment booms and other such supplementary deployment devices required in the past in connection with the deployment of both an RF reflector and a solar array on board a spacecraft.
The present invention takes advantage of a particular deployable RF reflector referred to as a foldable perimeter truss reflector. In the foldable perimeter truss reflector, RF reflective material is supported upon a truss, a framework of tubing and fittings that collectively form, as deployed, a short hollow three dimensional surface, such as a cylinder, often referred to as a hoop. The reflective material covers and lies over a circular end of that hollow cylinder, vaguely resembling a sagging drum head. The reflective material is a pliant reflective cloth-like fabric typically constructed of a cross hatch of wires welded together at the intersections or knitted gold plated molybdenum wire. It is light weight and pliant in nature, so it may be compacted as part of the stowed package. When the RF reflector is deployed, the fabric is stretched out on an end of the truss to form a parabolic curved surface.
To support and profile the shape of the pliant reflective mesh material, lines, referred to as caternaries, are strung from the periphery of the cylinder across the end and collectively define a parabolic surface shape. The reflective material is tied to those catenaries. It is pulled into the parabolic shape defined by those catenaries.
In the deployed condition as assembled, the foregoing cylindrical truss structure folds up for storage on board the space craft by collapsing inwardly toward the center, its various structural tubes and pivotal joints moving in unison in carefully orchestrated complex movements as the structure collapses inwardly, together with the accompanying reflective material, and culminates in an elongate cylindrical package that occupies only a small fraction of the space earlier occupied and is the non-deployed or stowed state.
The foregoing description only briefly describes the complex truss structure and its complex folding operation since they are already known to those skilled in the antenna art of that kind, and those details are not necessary to the understanding of the present invention and need not be presented here. The construction details for same are difficult even for those skilled in the art to use language to describe. For those readers unfamiliar with the subject it is believed impossible to visualize. For the interested reader, examples of such perimeter truss reflectors are found in the patent literature, such as U.S. Pat. No. 5,680,145 granted Oct. 21, 1997 to Thomson et al, assigned to Astro Aerospace Corp. A more comprehensive example is described in the application to Gilger and Parker, Ser. No. 09/080,767 filed May 18, 1998 now U.S. Pat. No. 6,028,570, entitled Folding Perimeter Truss Reflector, currently pending. The interested reader may refer to the foregoing patent literature for additional details of a foldable perimeter truss structure.
Photovoltaic arrays contain large numbers of photovoltaic cells, sometimes referred to as solar cells. The deployable array contains a plurality of solar panels that are joined together, may be folded up for stowage, and, upon command, may be unfurled for deployment. Each photovoltaic cell converts the energy in incident sunlight into electricity. The solar cells are arranged in series circuits and those series circuits are connected in parallel for the purpose of providing combining the outputs of each cell to collectively provide the appropriate levels of current at a sufficiently high voltage suitable for charging the DC batteries used on board the spacecraft.
The solar cells are formed of semiconductor material and have been formed on a thin pliant flexible film base that forms the support. That flexibility or pliancy thereby permits construction of deployable solar arrays. As in the case of the RF reflector, it is not necessary to describe those solar array construction details in the present specification, since they are not necessary to the understanding of the present combination invention and are known to those skilled in that field of endeavor. The interested reader is referred to the technical and patent literature for those details.